Phosphatase Subfamily PTPMT1

Phosphatase Classification: Superfamily CC1: Family DSP: Subfamily PTPMT1

PTPMT1 (or PLIP) is the first member of PTP superfamily found exclusively localized to the mitochondrion [1]. It was originally discovered as an open reading frame encoding a phosphatase with sequence similarity to the tumor suppressor PTEN [2]. Like PTEN, PTPMT1 possesses very poor activity toward proteinaceous substrates [2]. In vitro, it specifically dephosphorylates phosphatidylinositol 5-phosphate (PI5P), displaying much less activity against any other phosphoinositides [2]. However, depletion of PTPMT1 in cells produces no effect on the cellular level of PI5P, suggesting that PI5P is not the endogenous substrate [1]. Later, it has been found that PTPMT1 is a mitochondrial phosphatase that converts phosphatidylglycerolphosphate (PGP) to phosphatidylglycerol, a critical step in the de novo biosynthesis of cardiolipin [3]. It is found in most or all animals and higher plants, but is absent from fungi, Monosiga, and lower plants. It is also found in several protists, including Dictyostelium , Leishamania, Trypanosomes, Ectocarpus, and diatoms. More surprisingly, a functional PTPMT1 is found in a eubacterium Rhodopirellula baltica [4].

Acknowledgement. Thank Ji Zhang at UC San Diego for her contribution.

References

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